Bag-in-containers, also referred to as bag-in-bottles or bag-in-boxes depending on the geometry of the outer vessel, all terms considered herein as being comprised within the meaning of the term bag-in-container, are a family of liquid dispensing packaging consisting of an outer container comprising an opening to the atmosphere—the mouth—and which contains a collapsible inner bag joined to said container and opening to the atmosphere at the region of said mouth. The system must comprise at least one vent fluidly connecting the atmosphere to the region between the inner bag and the outer container in order to control the pressure in said region to squeeze the inner bag and thus dispense the liquid contained therein.
Traditionally, bag-in-containers were and still are produced by independently producing an inner bag provided with a specific neck closure assembly and a structural container (usually in the form of a bottle). The bag is inserted into the fully formed bottle opening and fixed thereto by means of the neck closure assembly, which comprises one opening to the interior of the bag and vents fluidly connecting the space between bag and bottle to the atmosphere; examples of such constructions can be found inter alia in U.S. Pat. No. 3,484,011, U.S. Pat. No. 3,450,254, U.S. Pat. No. 4,330,066, and U.S. Pat. No. 4,892,230. These types of bag-in-containers have the advantage of being reusable, but they are very expensive and labour-intensive to produce.
More recent developments focused on the production of “integrally blow-moulded bag-in-containers” thus avoiding the labour intensive step of assembling the bag into the container, by blow-moulding a polymeric multilayer preform into a container comprising an inner layer and an outer layer, such that the adhesion between the inner and the outer layers of the thus produced container is sufficiently weak to readily delaminate upon introduction of a gas at the interface. The “inner layer” and “outer layer” may each consist of a single layer or a plurality of layers, but can in any case readily be identified, at least upon delamination. Said technology involves many challenges, and many alternative solutions were proposed.
The multilayer preform may be extruded or injection moulded (cf. U.S. Pat. No. 6,238,201, JPA10128833, JPA11010719, JPA9208688, U.S. Pat. No. 6,649,121). When the former method is advantageous in terms of productivity, the latter is preferable when wall thickness accuracy is required, typically in containers for dispensing beverage.
The formation of the vents fluidly connecting the space or interface between bag and bottle to the atmosphere remains a critical step in integrally blow-moulded bag-in-containers and several solutions were proposed in, e.g., U.S. Pat. No. 5,301,838, U.S. Pat. No. 5,407,629, JPA5213373, JPA8001761, EPA1356915, U.S. Pat. No. 6,649,121, JPA10180853.
Preforms for the production of integrally blow-moulded bag-in-containers clearly differ from preforms for the production of blow-moulded co-layered containers, wherein the various layers of the container are not meant to delaminate, in the thickness of the layers. A bag-in-container is comprised of an outer structural envelope containing a flexible, collapsible bag. It follows that the outer layer of the container is substantially thicker than the inner bag. This same relationship can of course be found in the preform as well, which are characterized by an inner layer being substantially thinner than the outer layer. Moreover, in some cases, the preform already comprised vents which are never present in preforms for the production of co-layered containers (cf. EPA1356915).
One redundant problem with integrally blow-moulded bag-in-containers is the choice of materials for the inner and outer layers which must be selected according to strict criteria of compatibility in terms of processing on the one hand and, on the other hand, of incompatibility in terms of adhesion. These criteria are sometimes difficult to fulfill in combination as illustrated below.
Addressing processing compatibility, EPA1356915 and U.S. Pat. No. 6,649,121 proposed that the melting temperature of the outer layer should be higher than the one of the inner layer in order to allow production of integral preforms by injection moulding the outer layer thereof, followed by injecting thereover the inner layer. Examples of materials for the outer layer given by the authors include PET and EVOH, whilst polyethylene is given as an example for the inner layer. Though this materials selection could be advantageous for the injection moulding production of the preforms, it is far from optimal for the blow-moulding step since polyethylene and PET are characterized by different blow-moulding temperatures. Again, in U.S. Pat. No. 6,238,201 a method is described including coextruding a two layer parison followed by blow-moulding the parison into a bag-in-container wherein the outer layer preferably comprised an olefin and the inner layer an amorphous polyamide.
Concerning the materials choice for a weak interfacial adhesion required for ensuring proper delamination of the inner layer from the outer layer upon use, mention is made in JP2005047172 of “mutually non-adhesive synthetic resins.” In the review of the background art in U.S. Pat. No. 5,921,416 the use of release layers interleafed between inner and outer layers, forming three- or five-layer structures is mentioned. An example of such construction is described in U.S. Pat. No. 5,301,838 which discloses a complex five layer preform comprising three PET layers interleafed by two thin layers of a material selected from the group of EVOH, PP, PE, PA6. Here again, beside the complexity involved with the production of such preforms, substantial differences in blow-moulding temperatures characterize these different materials. Last but not least, the use of different materials renders recycling of such bag-in-containers problematic as the bag cannot be removed easily from the container after use.
It follows from the foregoing that there remains a need in the field of integrally blow-moulded bag-in-containers, with respect to the choice of materials for the inner and outer layers as well as for recyclability of the bag-in-containers after use.